/Engine/Source/Runtime/GeometryCore/Public/Implicit/CachingMeshSDF.h
Calculate twice signed area of triangle (0,0)-(X1,Y1)-(X2,Y2) return an SOS-determined sign (-1, +1, or 0 only if it's a truly degenerate triangle)
static int Orientation ( double X1, double Y1, double X2, double Y2, double & TwiceSignedArea )